1. Field of the Invention
The present invention relates to a method and system for detecting and correcting in-phase/quadrature imbalance in digital communication receivers. More particularly, the invention relates to a method for detecting and correcting amplitude and phase imbalance using simulation models.
2. The Background Art
A receiver is used to reprocess signal data received from a channel through undoing signal modifications made at the transmitter and the channel. Typically, the signal is distorted by the channel, as well as by internal and external causes. This distortion may be represented by a signal-to-noise ratio (SNR) defined as the ratio of the signal power to the noise power.
A modulated signal includes an in-phase component and a quadrature component. When the modulated signal is received, after conversion from an analog to a digital signal using an analog-to-digital converter, each bit is demodulated into the in-phase and quadrature signal components using sine and cosine functions. Typically, there is an amount of deviation in the proper alignment of the in-phase and quadrature components of the modulated received signal. This deviation may occur in both the amplitude and the phase of the in-phase and quadrature components of the signal. Moreover, imbalance is typically introduced by a tuner when the signal is received.
When a channel is changed or a channel is newly acquired, correction of signal imbalance is desirable. Typically, correction of the amplitude and phase imbalance is handled by hardware. For example, an equalizer may be used to correct interference present in the received signal. However, equalizers are expensive and not typically required to correct noise present in satellite receiving systems. A need exists for a method and system for first detecting and then correcting imbalance in the in-phase and quadrature signal components which may be implemented in software, significantly reducing the costs of such a system. Through the use of such a system, correction of imbalance may be performed off-line as the signal is being viewed.